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Clinical skills 2 > Microbiology of dental caries > Flashcards

Microbiology of dental caries Flashcards

1
Q

What is the composition of the dental microbiome in health?

A

Diverse composition of +700 species including bacteria, viruses, and fungi

The composition is relatively stable over time.

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2
Q

What process reduces microbial load on mucosal surfaces in the dental microbiome?

A

Desquamation

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3
Q

What surfaces permit heavy biofilm formation unless controlled?

A

Non-shedding surfaces such as teeth, dentures, and implants

These surfaces do not undergo desquamation like mucosal surfaces.

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4
Q

What are the features of multi-species biofilms?

A
  • Concerted and collaborative metabolism
  • Food chains
  • Cell-cell signalling
  • Environment modification (gradients)
  • Matrix formation
  • Balance achieved via complex interactions
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5
Q

What are the 3 main things that occur in symbiosis?

A

colonisation resistance

cross talk (immunomodulation)

entero-salivary nitrate circulatory system

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6
Q

What is colonisation resistance in symbiosis?

A

Exclusion of exogenous microbes

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7
Q

What happens during long-term antibiotic therapy in relation to symbiosis?

A

Leads to yeast overgrowth

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8
Q

What is cross-talk in the context of symbiosis?

A

Down-regulation of pro-inflammatory host responses while stimulating beneficial responses

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9
Q

What is the entero-salivary nitrate circulatory system?

A

Dietary nitrate -> nitrite -> acidified nitric oxide

This process can lead to decreased blood pressure and increased gastric mucus.

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10
Q

Which key oral microorganisms are associated with caries?

A
  • Streptococcus mutans
  • Lactobacilli
  • More acidogenic/acid-tolerating bacteria
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11
Q

What environmental factors contribute to caries as dysbiosis?

A
  • Cariogenic diet (frequent fermentable sugars)
  • Poor oral hygiene
  • Low saliva flow rate
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12
Q

What are some confounding factors in caries development?

A
  • Fluoride availability
  • Diverse natural microbiota
  • Non-specific virulence traits
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13
Q

What are the 3 main ways to characterise the oral microbiome?

A

traditional culture

microscopy

molecular approaches

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14
Q

What is a limitation of traditional culture in characterizing the oral microbiome?

A

Only 50-70% of oral microbiota can be cultured

This makes it laborious and expensive.

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15
Q

What microscopy techniques can be used to identify pathogens in the oral microbiome?

A
  • Conventional light microscopy
  • Electron microscopy
  • FISH (fluorescent in situ hybridization)
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16
Q

What are some molecular approaches to characterize the oral microbiome?

A
  • PCR
  • DNA-DNA hybridisation
  • Human oral microbiome identification microarray
  • High throughput whole genome sequencing (metagenomics)
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17
Q

What databases can support studies on the oral microbiome?

A
  • Human microbiome consortium
  • Human oral microbiome database
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18
Q

What are the findings from gnotobiotic animal studies?

A

some bacteria are more cariogenic

importance of fermentable sugars in diet

transmission from animal to animal

antimicrobial agents are studied - prevents caries

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19
Q

Describe cross-sectional studies

A

single time point for sampling

cheaper

only shows associations

We don’t know if caries is caused by increase in bacteria or caries itself causes an increase in bacteria.

We observe the sample at point of disease.

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20
Q

Describe longitudinal studies

A

has multiple time points for plaque sampling

which shows ‘cause and effect’ relationships.

We can observe sample from health to disease.

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21
Q

On what sample is vaccination carried out on?

A

rodents and primates

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22
Q

What are the characteristics of cariogenic bacteria?

A
  • Rapid sugar transport and acid production
  • Aciduricity (acid tolerance)
  • Extracellular polysaccharide
  • Intracellular polysaccharide
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23
Q

Name the implicated microorganisms in dental caries

A

streptococcus mutans

lactobacillus

bifidobacterium

veillonella

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24
Q

Describe mutans streptococci

A

Gram-positive cocci (short rods)

Found on hard non-shedding surfaces

Implicated in initiation of caries

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25
Describe lactobacillus
Gram-positive rod Implicated in advanced dental caries
26
Describe bifidobacterium
Gram-positive rod Branched cells Recently implicated in caries
27
Describe veillonella
Gram-negative coccus Anaerobic Utilises lactic acid in plaque and produces propionate / acetate
28
What does base-generating bacteria do?
neutralise effects of cariogenic bacteria are arginolytic and inhibit mutans streptococci
29
Name some base generating bacteria
S. salivarius, S. sanguinis, A. naeslundii new species S. dentisani S. A12.
30
How does base-generating bacteria use urease?
Urea + H2O -> ammonia + CO2
31
How does base-generating bacteria use arginine deaminase system?
Arginine -> citrulline + ammonia -> ornithine + carbamyl-P -> ATP + CO2 + ammonia
32
What type of caries has mutans streptococci and lactobacillus been found to cause? What are some associated bacteria?
nursing bottle caries / early childhood caries scardovia wiggsiae and slackia exigua
33
What bacteria is found in biofilms of non-carious, healthy tooth surfaces?
- Streptococcus cristatus - S. gordonii - S. sanguinis - Corynebacterium matruchotii - Neisseria flavescens
34
What bacteria has been implicated in root caries?
Early studies: actinomyces spp Later studies: mutans streptococci, lactobacilli Recent studies: actinomyces spp (actinomyces israelii and A.gerencseriae), mutans streptococci, gram negative rods
35
Other than cariogenic, what other qualities of bacteria cause it to produce cavitation when reaching dentine?
proteolytic and collagenolytic
36
What are some challenges of understanding microbiology?
Disease occurs at sites with natural and diverse microbiota Pathogens are also found at healthy sites – often as minor component of multi-species biofilms Difficult to correlate microbiota to enamel status Lesions can remineralise Pathogenic traits are relatively non-specific Multi-factorial nature of caries (key oral micro-organisms, susceptible host, environmental factor)
37
What has been observed at cross-sectional human studies?
- Mutans streptococci increases at caries sites - There is an inverse relationship between MS and S sanguinis - Some sites with caries have no MS, some sites with caries have MS In fissure caries... - 71% had >10% MS over total cultivable microbiota - 70% of caries-free fissures had no detectable MS
38
What has been observed in longitudinal human studies?
- MS does increase at caries sites - MS can occur after first signs of demineralisation - Caries can occur in absence of MS - The role of other species in caries progression eg lactobaccili in advanced lesions
39
Is the microbial aetiology diagnostic of caries/gingivitis?
no normally yes
40
Is the pathogen present in health in caries/gingivitis?
yes/often normally no
41
Does the pathogen satisfy Kosch's postulates in caries/gingivitis?
no normally yes
42
Does the pathogen produce specific virulence factors in caries/gingivitis?
no normally often
43
Is caries/gingivities transmitted person-to-person?
no normally yes
44
How does dysbiosis occur?
Factors ... - major ecological pressure - frequent sugar intake - reduced saliva - acidic pH ... contributes to development of dysbiosis in oral microbiome gives rise to the cariogenic microbes
45
What do the cariogenic microbes in dysbiosis do?
- Acid production - Tolerate acid - Extracellular polysaccharide and intracellular polysaccharide production (EPS / IPS)
46
What does the ecological plaque hypothesis suggest the disease is caused by?
- Direct inhibition of causative organisms - Promotion of natural balance (symbiosis) - Interference with factors driving dysbiosis Specificity in disease is found in microbial function and not bacterial name Aetiology isn’t mono-specific as many species can contribute
47
What are the 3 functions of sucrose?
sticky slime (EPS in biofilm matrix and microbial attachment) food reserves (IPS when dietary sugars are absent) fermentation products (lactic acid, other acids and energy produces acidic pH)
48
What are some approaches to control dental caries?
Plaque control Fluoride Sugar substitutes Antimicrobial and anti-plaque agents Modify the microbiota (prebiotics) Vaccination Passive immunisation
49
What role does fluoride play in dental caries?
- forms fluorapatite mineral - Acidify cell interior (H+F-) - Inhibit IPS synthesis - Reduce glycolysis and acid production - Remove competitive opportunity for mutans streptococci and other acid-loving bacteria by eliminating low pH environment
50
What are 2 substitutions for sugar?
bulking agents (eg sorbitol, xylitol) or intense sweeteners (eg saccharin, aspartame)
51
What effect do sugar substitutes have?
not, or weakly, metabolised to acids they stimulate saliva flow Weak antimicrobial activity is associated with these substitutes.
52
Where can sugar substitutes be found?
beverages, confectionary, chewing gum.
53
In classic medical, there is a single pathogen - what about conventional dental?
mixed community / biofilm
54
In classic medical, there is a sterile site - what about conventional dental?
site with resident beneficial microbiota
55
In classic medical, the diagnostic microbes are absent in health - what about conventional dental?
present in health
56
In classic medical, bactericidal drugs are preferred - what about conventional dental?
below minimum inhibitory concentration is effective
57
What forms can antimicrobial and antiplaque agents appear?
- toothpastes and mouthwashes - chlorhexidine (gold-standard as it’s antiplaque and anti-mutans streptococci) - triclosan, metal salts, plant extracts, enzymes, innate host defences - agents can generate alkali eg arginine - MIC v sub-MIC effects eg inhibit glycolysis, sugar transport
58
How are antimicrobial agents applied?
once or twice daily either for a short duration but at a high concentration or slow release during long duration at a low concentration
59
Describe streptococcus dentisani
arginolytic produces ammonia
60
Describe streptococcus A12
bacteriocin inhibits MS
61
62
Why does the mouth have the components for a full immune response?
- sIgA (saliva) - IgG - Neutrophils - Complement in GCF
63
What 3 things are vaccines based on?
whole cells, glucosyltransferases, cell wall associated protein
64
How is passive immunisation carried out?
coating the tooth surfaces with antibodies or synthetic antibody fragments reduces MS colonisation in humans and primates

Clinical skills 2 (20 decks)

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